1. Field of the Invention
The present invention relates to a sound motion picture projector.
2. Description of the Prior Art
There are many films for recording both image data and sound. There are two methods for recording sound on the film, namely optically and magnetically. In accordance with the former it is impossible to erase the sound recorded on the film or to record a new sound thereon. In accordance with the latter the original sound can easily be erased, and new sound can easily be recorded. Moreover, the new sound can easily be made to overlap the original sound.
However, until several years ago, 8 mm films on which sound information was recorded magnetically had not yet been brought on the market so that the sound information was recorded on the films optically. Consequently, all sound motion picture projectors for the 8 mm size film reproduced sound optically.
Quite recently 8 mm sized films on which the sound can be recorded magnetically have been brought on the market under the trade name "Sound Movie Film" by Eastman Kodak Company, U.S.A. sound motion picture cameras by which sound information can be recorded magnetically as well as sound motion picture projectors by which sound information can be reproduced magnetically have also been actively developed.
As is disclosed in U.S. Pat. No. 3,858,968, the afore mentioned sound movie film has a main stripe of magnetic recording material along one side edge of one surface of the film and a balance stripe of magnetic recording material along the other side edge of the same surface; The balance stripe is located adjacent to a series of perforations in the film while the light sensitive emulsion on the film is usually located on the opposite (lower side) surface of the film.
The reason why this film is provided with a balance stripe beside the main stripe is that if only the main stripe is coated on the base material of film, the wound up film coil slants. Thus in order to compensate for the difference in thickness between both edges of the film, the balance stripe is coated.
Consequently, the sound information is normally recorded only on the main stripe serves while the balance stripe exclusively to compensate for the difference in thickness between both edges, not to record the sound information. This is not because sound information can not be recorded on the balance stripe but because the width of the balance stripe is so small as compared with that of the main stripe that the quality of the reproduced sound is inferior when the sound is recorded on the balance stripe. Thus, it is also possible for sound information to be recorded on the balance stripe if the lowering of the sound quality is disregarded. A motion picture system in which the sound information is recorded on both the main stripe and the balance stripe is disclosed, for example, in DOLS 2,417,095. In accordance with the application disclosed in DOLS 2,417,095, the image information is first recorded on a film on whose main stripe the sound information supplies the background-music, while the sound information corresponding to the above image information is recorded on the balance stripe. Then, making use of an editor having a recording-reproducing head corresponding to the main stripe and the balance stripe of the film, the sound edition is made by overlapping the sound recorded on the balance stripe on the sound such as a background-music recorded in advance on the main stripe, or a part of the sound information on the main stripe is deleted and in its stead the sound information on the balance stripe is recorded.
It is normal in the field of tape recording that the sound edition is made by repeatedly recording sound information over what is already recorded on a tape. This editing method is called "sound on sound" or "sound with sound".
In accordance with the "sound on sound" method applied in the field of tape recording, the sound information recorded in advance on the first track of the magnetic tape is reproduced by means of the recording-reproducing heat reproducing the first track into an audible signal. This signal is newly recorded, further overlapped with a bias current and delivered to the recording-reproducing head provided for the second track of the magnetic tape so as to be recorded on the second track. Thus the original signal and the newly-recorded are synchronized with each other, and in reproduction the both signals on the second track are heard by reproducing the mixed signals. On the other hand, in accordance with the "sound with sound" method the original sound signal on the first track is reproduced by means of the first recording-reproducing head into an audible signal, while at the same time a newly-recorded sound signal is overlapped with a bias current and delivered to the second recording-reproducing head provided for the second track of the magnetic tape. Thus the newly-recorded signal a signal to be recorded is recorded on the second truck in is synchronized with the original signal. At the time of reproduction the sound information on the first and second track are reproduced simultaneously such that both signals are audible, being mixed with each other. However, in case of the "sound on sound" method and the "sound with sound" method applied in the field of tape recording, it is necessary, as mentioned above, that the magnetic tape include at least two tracks. These methods are not applicable to a device including only one track.
However, the aforementioned magnetic recording film on which the sound and the image are recorded so small in the has such a narrow width of the main stripe that only one track can be constituted. Thus it is impossible to apply the "sound on sound" method or the "sound with sound" method as in the field of tape recording, as a sound editing method. Consequently in the case of the conventional sound motion picture projector the demagnetizing head and the recording-reproducing head are provided in sequence from the film fowarding direction along the film running path. For "double recording" the demagnetizing head inoperative and a new sound information signal overlapped with a bias current is delivered to the recording-reproducing head. For a "complete deletion recording" both the demagnetizing head and the recording-reproducing head are operative. In the case of "double recording", when the film passes through the position at which the demagnetizing head is arranged, the original sound information signal recorded on the main stripe of the film is deleted. Then the new sound information signal is recorded on the main stripe when the film passes through the position at which the recording-reproducing head is arranged.
However, in order to carry out the "double recording" or the "complete deletion recording" the afore mentioned conventional sound motion picture projector, it is necessary to find out, by means of a flair, the position at which the "double recording" or the "complete deletion recording" is to be carried out. This is because the picture projector is not designed to produce an audible signal from the already-recorded sound to indicate when new sound information may be recorded. Consequently, with a wrong mark, the necessary sound information is apt to be deleted by mistake or unnecessary sound information remains undeleted in the case of the "complete deletion recording", which is inconvenient. In the case of "double recording", a double recording with wrong timing is obtained, which is also inconvenient. Thus, it is remarkably difficult to use the projector for correct sound edition, which is problematic.
It might be possible to solve the problem of sound edition with the conventional sound motion picture projector with just one magnetic recording means. A previously recorded track could be reproduced into an audible signal, indicating when new sound information should be supplied. For example one might arrange the reproducing head, the demagnetizing head and the recording head in sequence from the forwarding direction of film. Thus for "complete deletion recording" the original sound signal is reproduced my means of the reproducing head, then deleted by means of the demagnetizing head. While the reproduced signal is being heard it is mixed with the new signal to be recorded, overlapped with a bias current and then delivered to the recording head provided behind the demagnetizing head. Thus the new signal is recorded in synchronization with the original signal. In the case of the "double recording" demagnetizing head is operative. The sound signal recorded in advance is heard through the reproducing head while the signal new is overlapped with a bias current and delivered to the recording head so that original the signal and the new signal are recorded on film, in synchronization. However, the above system can not be applied to the sound motion picture projector for which the relative position between the picture and the sound has been determined because the position of the original sound signal before "sound on sound" is displaced from the position at which the new signal is recorded by the distance between the reproducing head and the recording head.